The assignee of the present invention has recently developed torsionally hinged mirrors with a single reflection surface as described in U.S. patent application Ser. No. 10/384,861 and entitled “Laser Printer Apparatus Using a Pivoting Scanning Mirror”. This dual axis mirror uses a first set of torsional hinges for moving a beam along a first axis such as a pivoting or resonant beam sweep and a second set of torsional hinges that selectively moves the pivoting beam sweep in a direction orthogonal to the first axis. By dynamically controlling the orthogonal position of the moving beam, both directions of the pivoting beam may be used to generate parallel image lines. Alternately, two single axis mirrors can be arranged such that one mirror provides the back and forth beam movement and the other mirror controls the orthogonal position of the beam sweep.
As will be appreciated in the semiconductor processing art, the number of devices that can be produced on a wafer (i.e. yield) is one of the important considerations if an acceptable profit margin is to be achieved. To date, the size of the functional surface or reflective surface of a MEMS device, such as a mirror, has been significantly less than the overall size of the device. The outside support frame typically determines the overall dimension of the device and is often several times larger than the functional or reflective surface. It would be advantageous and increase yield if the overall size could be reduced while keeping the functional surface the same size.
For mirror devices manufactured according to this invention, it will also be appreciated by those skilled in the art that controlling the orthogonal (vertical) position of the oscillating or resonant scan will allow a single surface or flat oscillating mirror to be used to provide a moving light source for laser printers or a full frame of raster scans suitable for use on consumer projection displays including micro projection displays such as cell phones, Personal Digital Assistants (PDA's), notebook computers and heads-up displays. Of course, if such displays are to be commercially acceptable, they must be small, low cost, robust enough to withstand greater than 1000 G's of shock, and stable over the operating temperature normally experienced by hand-held products.
Consequently, it will be appreciated that a high frequency scanning mirror is a key component to the success of such optical products manufactured according to this invention. Further, since many of the applications for such projection displays are battery powered, all of the components (including the scanning mirror) must be energy efficient.
As mentioned above, Texas Instruments presently manufactures a two axis analog mirror MEMS device fabricated out of a single piece of material (such as silicon, for example) typically having a thickness of about 100-115 microns using semiconductor manufacturing processes. The layout consists of a mirror having dimensions on the order of a few millimeters supported on a gimbals frame by two silicon torsional hinges. The gimbals frame is supported by another set of torsional hinges, which extend from the gimbals frame to a support frame or alternately the hinges may extend from the gimbals frame to a pair of hinge anchors. This Texas Instruments manufactured mirror with two orthogonal axes is particularly suitable for use with laser printers and/or projection displays. The reflective surface of the mirror may have any suitable perimeter shape such as oval, rectangular, square or other. It should also be appreciated that devices having functional surfaces other than mirror or reflective surfaces may be manufactured according to the teachings of this invention.
A similar single axis device may be fabricated by eliminating the gimbals frame altogether and extending the single pair of torsional hinges of the device directly to the support frame or support anchors. Two single axis devices rather than one dual axis device may then be used to generate bi-directional movement, but may require more space.
One presently used technique to oscillate a device about a first axis is to provide an electromagnetic coil on each side of the mirror and then drive the coils with an alternating signal at the desired sweep frequency to alternately magnetically attract portions of the device on opposite sides of the pivot axis. Electromagnetic coils may also be used to provide the orthogonal movement so as to achieve bi-directional movement. In addition, the device can be made to pivotally resonate about its axis in response to electromagnetic excitation. Such resonant motion is particularly advantageous when the bi-directional device is a mirror used in printers or various display devices. However, other techniques of generating vibrations in the mirror structure to cause the device to pivotally resonate about its axis may be used. These other techniques may include electrostatic drives, piezoelectric drives and the like.